Conventional clothes dryers heat a large volume of air that then passes over tumbling clothes. Water is extracted from the wet clothes by evaporation into the heated air. This conventional drying process is extremely inefficient, as most of the energy consumed by the dryer goes out a vent.
This invention is a new way to use low frequency RF (roughly 10 MHz to 100 MHz) capacitive electrical energy to replace the conventional forced hot air clothes dryer that has been used since it was introduced almost 75 years ago. In the present invention, water is evaporated by heat of friction of the water molecules vibrating at the RF frequency. The resulting water vapor is carried away by forced air. The wet clothes load appears as a capacitive electrical element through which the low frequency RF current flows, exciting the molecules of water so that their energy is raised above the heat of vaporization, causing a state change from liquid to vapor.
A number of approaches have been presented that use electrical, magnetic, or electromagnetic energy to dry fabrics, all of them with inherent inconveniences and/or shortcomings due to failure of the designers to comprehend optimum means to couple RF energy to the drying fabrics.
For example, W. N. Frye in U.S. Pat. No. 2,511,839 issued Jun. 20, 1950 describes a “Method and Apparatus for Drying Textile Materials by High-Frequency Electric Fields” where the requirements are for a nonconductive container drum. Frye's drum needs to be non-conductive (i.e., insulating) for the electric fields to reach the load, because his electrodes are rings or coils set up OUTSIDE of the clothes drum (if it were a metallic drum, it would act as a Faraday shield to the load, and no energy would be transmitted through it). This condition applies to the embodiments disclosed in Frye's FIGS. 1,2,3,4 and 10. In the embodiment disclosed in FIG. 4, Frye uses a couple of plate electrodes instead of rings, but they are also positioned outside the drum (attached to the insulating member that surrounds the drum, column 4, lines 13-14). While Frye develops heating energy by applying a high frequency electric (or magnetic in other embodiments) field to the load, he does not disclose a frequency of operation, a tuning network, or a means to detect the degree of humidity or other parameters as the drying proceeds as in the present invention. Furthermore, in many embodiments of the present invention, the drum is electrically conductive.
In the embodiment depicted in FIGS. 7 and 8, one of Frye's electrodes seems to be statically positioned inside the drum, like a cantilever beam, but secured to the front wall of the machine (column 6, lines 14 to 22), with the drum rotating around it. The other electrode is placed outside the drum (column 6, lines 22 to 26). There is no physical contact of the electrodes with the load. Both electrodes are separated from the load; thus, coupling is reduced by the introduction of an additional air series capacitance that reduces the amount of current flowing through the load.
Eran Ben-Shmuel et al., in U.S. published patent application US2010/0115785 A1 published May 13, 2010, describes a “Drying Apparatus and Methods and Accessories for Use Therewith” that consists of using multiple frequencies of electromagnetic RF energy set up in a cavity to dry clothes and heat foods. Ben-Shmuel uses an antenna to couple the field energy to the load. Ben-Shmuel teaches the use of a high frequency (>300 MHz) RF field to excite electromagnetic fields in a cavity. The present invention does not require a cavity with dimensions related to the wavelength of the applied RF energy as in Ben-Shmuel. Rather, the present invention seeks to maximize current flow though the capacitive coupled load.
Joseph A. Gauer, in U.S. Pat. No. 5,463,821 issued Nov. 7, 1995, describes a “Method and Apparatus for Operating a Microwave Dryer,” which discloses inserting microwave magnetrons in the dryer impellers to provide the heating energy. Again, this is another high frequency approach as in Ben-Shmuel.
Tsui et al. in U.S. published patent application US2007/0045307 A1 published Mar. 1, 2007, describes a “Radio Frequency Textile Drying Machine,” a stationary drum that can function as a cathode (or anode) having an anode (or cathode) spindle where wet textiles (supposedly in strips or yarn) are placed and are subjected to a 27 MHz RF field, to excite water molecules and create heat to evaporate the moisture. Air flow is provided to remove the moisture from the apparatus. There is a substantial air gap between the spindle and its yarn strip, and the drum. This air gap acts as a small capacitance (high reactance) in series with the capacitance (and parallel resistance) of the wet yarn, greatly reducing the amount of current available to add energy to the water molecules in the yarn. The present invention has no such energy-draining air gap. Also, Tsui does not disclose the present invention's dynamically matching network for efficient RF energy transmission to keep up with the impedance of the load changing as the load dries and loses water.
Serota, in U.S. Pat. No. 3,866,255 issued Feb. 18, 1995 entitled “Dielectric Apparatus for and Methods of Treating Traveling Paper Webs and the Like”, discloses a flat arrangement of alternating anode and cathode bars (or a flat cathode plate) over which wet paper (in sheet form) is passed and heated by RF energy (no frequency specified, and no air blowing). In one embodiment of Serota, some tuning is obtained by a variable inductor and a moving capacitor plate that also serves as an RF connection to the anode bars.
These prior art approaches have not been practical, because of the difficulties of providing a non-conducting drum container; the fact that a cavity used as a drum limits the drum size due to the constraints to set up an electromagnetic field inside; non specificity of the optimum frequency range to use for optimum drying; and the problems that metal objects (such as zippers and buttons) have in overheating in high frequency RF and microwave fields.